1. Field
Aspects of the present invention generally relate to a monitoring system, a wayside light emitting diode (LED) signaling device, and a method for monitoring a wayside LED signaling device.
2. Description of the Related Art
The railroad industry, including but not limited to the freight railroad industry, employs wayside lights to inform train operators of various types of operational parameters. For example, colored wayside signal lights are often used to inform a train operator as to whether and how a train may enter a block of track associated with the wayside signal light. The status/color of wayside signal lamps is sometimes referred to in the art as the signal aspect. One simple example is a three color system known in the industry as Automatic Block Signaling (ABS), in which a red signal indicates that the block associated with the signal is occupied, a yellow signal indicates that the block associated with the signal is not occupied but the next block is occupied, and green indicates that both the block associated with the signal and the next block are unoccupied. It should be understood, however, that there are many different kinds of signaling systems. Other uses of signal lights to provide wayside status information include lights that indicate switch position, hazard detector status (e.g., broken rail detector, avalanche detector, bridge misalignment, grade crossing warning, etc.), search light mechanism position, among others.
Existing wayside signals including incandescent bulbs are lit from either vital relay-based systems or vital processor-based systems that are available from a wide variety of manufacturers. The two basic types of systems have different interface characteristics, and interface characteristics vary substantially within the various processor-based systems. The systems permit hot and cold filament checks in order to detect lamp malfunction. Hot-filament checking implies verifying that sufficient visible light is being emitted when the appropriate input is provided to the signal head. Cold filament checking is similar, but is a check done when the aspect is not illuminated. This provides advance knowledge of a lamp failure so that the preceding aspects can be downgraded in advance, thus preventing a sudden unexpected downgrade.
Wayside signaling is moving away from incandescent bulbs to LED (light emitting diode) lighting. The benefits of wayside LED signals are improved visibility, higher reliability and lower power consumption. However, current wayside LED signaling devices are incapable of providing real time light out indication, i.e. lamp malfunction, in particular when utilizing a LED retrofit design for existing signal heads. For example, LED driver circuitry does not permit the current methods of hot and cold filament checks of incandescent bulbs. An option for retrofitting existing signal heads with LED lighting is to use microprocessor-based systems to monitor the status of the wayside signals. But such an upgrade requires extra installation, maintenance, and operational costs. Also, there are solutions that utilize a lamp unit input sensing resistor to verify operation. But this solution introduces an undesirable heat byproduct to the signal housing. Thus, the railroad industry and railroad owners wishing to upgrade their in-service wayside signaling heads by retrofit must choose LED lighting and losing light out detection or incandescent signaling bulbs with light out detection.